There are electric loads requiring for their starting-up or switching-on a current, known as “start-up current”, which can reach values which cannot be supplied by some types of power devices adapted to drive loads. Particularly, lateral flow power transistors, such as those manufactured by the BCD technology (Bipolar CMOS DMOS), as opposed to VIPower transistors, may not be capable of sustaining start-up currents of some types of loads, such as those used, for example, on motor vehicles, incandescent lamps or, generally, linear loads. These power transistors, operating as switches, manage the starting-up or switching-on step of the load by applying the auto-recovery mode.
According to the auto-recovery mode, when the current absorbed by the load reaches a predetermined threshold value, the power transistor is switched many times between the switching-off and starting-up, to supply the load with a current having a PWM-type trend and taking a maximum value not greater than the threshold value. The average current supplied to the load in the auto-recovery mode is such as to take it, during a suitable time range and without anomalies, to the standard operation. Indeed, when the maximum current absorbed by the load in a PWM cycle is less than the threshold value, the auto-recovery mode is interrupted and the power transistor remains switched to supply a nominal current to the electric load.
Electronic circuits on which power devices for driving electric load are integrated, offering the capability of operating in an auto-recovery mode, are often managed by a microcontroller outside the integrated circuit, such as, for example, the central unit of a car. Typically, such an outer or external microcontroller is capable of adopting protection provisions entailing the switching-off of the power devices in the presence of particular abnormal conditions.
Moreover, power devices, such as MOSFETs, driving loads have the capability of switching off when non-sustainable junction temperatures are reached, by performing a so-called thermal shut down. The occurrence of abnormal operation conditions are observed in which the power transistor does not supply the load which it was designed for, but instead supplies a short-circuit or an overload.
According to standard driving techniques, the short-circuit or overload conditions leading to an overcurrent state, are managed based on the auto-recovery mode until the occurrence of a temperature increase such as to cause the thermal shut down.